A cellular phone terminal and a cellular phone network using the third-generation W-CDMA technique use a circuit switching network or the protocol of circuit switching in order to realize a voice telephone and a TV telephone.
On the other hand, there is a movement to provide multimedia service on such a circuit switching network by using an IMS on an IP network. In the future, various services are going to be unified on an IMS core network. The configuration of an IMS is described in, for example, Non Patent Literature (NPL) 1 specified by 3GPP (3rd Generation Partnership Project) which will be described later and TS23.228.